The Internet enables access to a wide variety of resources, such as video or audio files, web pages for particular subjects, book articles, or news articles. A search system can identify resources in response to a user query that includes one or more search terms or phrases. The search system ranks the resources based on their relevance to the query and importance and provides search results that link to the identified resources, and orders the search results according to the rank.
A search system uses a search operation to identify resources that are responsive to the query. The search operation takes into account features of the resources and the query, and perhaps other information, when generating search scores for the resources. Typically the search operation implements a robust search algorithm that performs well over a wide variety of resources. However, sometimes particular features for a particular query and a particular set of resources may be quite important in determining the search scores for the resources, while for other queries the particular features may be much less important. For example, for a particular query with certain terms, the presence of those terms in the resources may have a very strong impact on the search scores for the resources; conversely, for another query with different terms, the relative importance of the resources in an authority graph may have a much stronger impact on the search scores than the presence of query terms in the resources. However, the relative importance of particular features for particular queries and resources is often difficult, if not impossible, to predict a priori.